function zukang_stright = stright_road(n,flag)
global e_2;
x_i2 = e_2 /100 / 92;
if flag == 1
    zukang_stright = 30 * (1 + 0.15 * (n / e_2) ^ 0.4)...
           + (10 * (1 - 0.5 ) ^ 2) / (2 * (1 - 0.5 * x_i2)) ...
           + (x_i2 ^ 2) / (2 * n * (1 - x_i2))...
           -  0.65 * ((10 / (n ^ 2)) ^ (1/3)) * (x_i2 ^ (2 + 5 * x_i2));
else
    zukang_stright = (10 * (1 - 0.5 ) ^ 2) / (2 * (1 - 0.5 * x_i2)) ...
           + (x_i2 ^ 2) / (2 * n * (1 - x_i2))...
           -  0.65 * ((10 / (n ^ 2)) ^ (1/3)) * (x_i2 ^ (2 + 5 * x_i2));
end
end

